Preformulated Implementation Intentions to Promote Colorectal Cancer Screening: A Cluster-Randomized Trial

Objective: To evaluate an intervention based on implementation intention principles designed to increase uptake of colorectal cancer screening, and to examine differential efficacy by socioeconomic deprivation. Method: In England, adults aged between 60 and 69 years are invited for biennial fecal occult blood testing. A test kit and an information leaflet are mailed to each individual by the Hubs that deliver the national screening program. In the intervention group, three preformulated implementation intentions, based on known barriers to carrying out the test, were added to the information leaflet. Over a 12-week period, each week was randomly allocated to either the intervention (n = 12,414 invitations) or the control condition (n = 10,768), with uptake recorded at the Hub. Socioeconomic deprivation of each individual's area of residence was categorized into tertiles. Results: There was no overall difference in uptake between control (40.4%) and intervention (39.7%) conditions, odds ratio (OR) = 0.97, 95% confidence interval (CI) [0.91, 1.04]. There was an interaction with deprivation, OR = 1.11, 95% CI [1.04, 1.18], but the positive effect observed in the lowest socioeconomic status (SES) tertile was small (35.2% vs. 33.0%), OR = 1.103, 95% CI [1.01, 1.21], and offset by a negative effect in the least deprived tertile (45.6% vs. 48.2%), OR = 0.90, 95% CI [0.82, 0.99]. The intervention had no significant effect in the middle tertile (38.9% vs. 40.8%), OR = 0.92, 95% CI [0.81, 1.04]. Conclusion: Preformulated implementation intentions did not increase overall colorectal cancer screening uptake and failed to make a sufficiently large impact on uptake among lower SES groups to merit their future use in this context.